Custom form component to featured

Hi Alex,
These are meant for predefined Kentico fields only, there is currently no way to add those.
You could try to have a look into the table CMS_FormFeaturedField though, where the configuration for these fields are located. No guarantees adding your own here though, but it might be worth giving it a try, or submit a feature request at https://roadmap.kentico.com

Disabling (some) featured fields can be done here: /admin/forms/featured-fields